Telephone transmitter and receiver



Aug. 3 1926.

. 1,594,802 A. F. SYKES TELEPHONE TRANSMITTER AND RECEIVER Filed July 21, 1924 2 Sheets-Sheet l J E J F I F D q I M I 1 $7 [I Z 5; 7

INVENTOR:

ADRIAN FRANCIS sms, By his Attorneys,

B -Ma Aug. 1926.

A. F. SYKES TELEPHONE TRANSMITTER AND RECEIVER Filed July 21, 1924 2 Sheets-Sheet 2 INVENTOR:

ADRIAN FRANCIS SEES By his Attorneys,

Patented Aug. 3, 1926.

UNITED "STATES.

PATENT, oFrIcn.

ADRIAN FRANCIS. SYKES, OF NEW BARNET, ENGLAND.

TELEPHONE TRANSMITTER AND RECEIVER.

Application filed July 21, 1924, Serial No. 727,242, and in Great Britain February 11, 1921.

This invention relates to telephone transmitters and receivers.

My British specification No. 160,223 described the employment of electric circuits for distorting the currents produced by the influence of sound waves on a detector or transmitter in order to give the higher frequencies their proper proportionate effect. By the present invention I am enabled to dispense either wholly or in part according to circumstances with the circuital arrange- .ments for obtaining systematic distortion as described in that specification.

According to my invention I combine with a conducting winding or membrane, which is in effect non-resonant and is immersed in a magnetic field, a barrier or means for restricting the motion of the air particles which convey the sound waves.

Preferably the conducting winding or membrane is arranged in front of acavity or channel formed in material which permits a strong magnetic field to act upon such winding or membrane and which is of sumcient mass as to render it relatively nonresonant to the sound waves compared with the much lighterdetecting membrane.

For instance, a sheet of thin metal foil or leaf may be supported in front of a shallow cavity or channel in a massive shield of bronze which may be placed between the poles of an electromagnet. When sound waves fall upon such foil :2. potential is developed therein and this may be transformed up and control the grid of the first valve in a relay system. The shield restricts the motion of the air particles in its immediate vicinity more in the case of iow frequencies than in the case of high frequencies, so that a relatively greater potential will be developed in the foil by sound waves of shortlength than by long waves. Thus the'result of the appliance may be regarded as a differentiating process. Such an appliance may also be used as a receiver, that is to say, telephonic currents may be applied to the winding or membrane to cause it to vibrate and generate sound waves, and in this case there is a greater tendency of the air in front of the strip to slip round to the back of the strip for low frequencies than for high frequencies. In consequence of this with suitable design the receiver and the transmitter yield a nominally true reproduction of the original sounds merely with an amplifier connecting the two instruments and without further correction. The size of the reflecting surface set at the back of the detecting membrane has some bearing on the properties of the instrument; a small reflecting surface yields higher pitch speech than one of larger dimensions because the local effects due to the obstruction of the instrument itself depend on the size of the instrument up to a point. It is obvious that a horn may be used to increase the effects whether the instrument is used as a transmitter or receiver.

Figures 1 and 2 are diagrammatic views illustrating the invention by showing the difference in. principle between a previous apparatus and the present one.

Figures 3 and 4 show an embodiment of of an electromagnetic telephone constructed on the lines set forth in my British specification No. 160,223. Only the rudiments of the apparatus are indicated in order to distinguish more clearly the feature which differentiates the apparatus of this my present invention from the apparatus described in the basic patent. It will be seen that for the purpose of this argument the sound reproducing apparatus comprises in essence magnetic poles A and B, a coil C itself forming the sound reproducing element, an obstruction D generally constituted by the field magnet winding and a sound channel E which conveys the sound not intercepted by the coil 0 when transmitting or receiving. lhe double ended arrows indicate the alternating character of the vibrations ofenergy is limited to the small space F at the rear of the conducting element C. When sound acts on this arrangement the pressures resulting from the reflection of the wave by the surfaces D and C relatively pends on the simultaneous difference of the pressures established immediately in front or to the rear of'the element C. The effect of the combination of element G, the free passageway G and the cavity F is to delay the establishment of a pressure effect in the cavity corresponding to the pressureefl'ect .in front of the element 0, in other words,

the device establishes a difference of phase between the front and the rear of the sound reproducing element, which phase difference construction a cobalt steel permanent mag is dependent on the frequency.

Figures 3 and 4 show an elevation and section respectively of an instrument constructed according to my inwention. In this net H is clamped toa bronze casting J by a bronze plate K and b the polar'extensions A and B, or is 0t erwise fixed relatively to the bronze casting. A strip of aluminium foil 0 is in electrical contact with the bronze casting at I: and insulated from and clamped to the casting by the system of plates and insulators L. The potential developed in the strip G by the action of the impinging. sound isapphed to the potential transformer M via the leads N; conversely,

telephone currents or derivatives thereof are supplied by this transformer when the apparatus is used as a receiver. Rubber straps A or cables 0 attached to the lugs P serve atone and the same time to insulate-the instrument when used as a transmitter from ex-.

traneous vibration and also as a means. of support. To avoid eflfects due to the foil not *beingl perfectly flat a number ofslits are usua y cut inthe foil as shown and the whole .surface is smeared with Vaseline or the like. -As the cavity or channel behind the strip may give trouble by acting as a resonator we may fill this cavity space or channel E with a sound absorbing medium, such as asbestos wool, pile velvet, *cotton wool, in similar fashion to the use of the sound absorbing medium used in the h drophone described in the Sykes Morris B;

sirable to use for this purpose pilevelvet which does not quite touch the sensitive element but otherwise fills the space.

Fi res 5 and 6 are side and front'views of a orm of instrument specially adapted to operate with a coil of many turns.

In this instrument an electromagnet is used to provide the field and the energizing I itish" specification No. 127,296.- I may find it de-" winding Dv also takes theplace of the casting J of Figures 3 and 4. Numerous ex periments have shown that a convenient and effective method of supporting the coil C aperiodically is to stick it with the minimum of adhesive to a pad of cotton wool Q; in these circumstances the coil C is so lightly constrained that its natural period of vibration is far below frequencies of acoustic value. The polar ring R is attached by screws to the magnet limbs and also to gun metal covers which together with the mag- .net limbs completely encircle the windings.

The diameter of this ring B may be SIX inches and the coil C may be one quarter of an inch from the windin D. In Figure 5 these are omitted showing the general construction, while in Figure 6 their position is indicated by dotted lines; some of the screws enter the magnet casting, others enter the gun metal covers. In another construction I make the field magnet itself in the form of a pot of cast iron. Wires from the sensitive coil are brought out to insulated'terminals S. I do not limit myself to any particular method of mountingthe coil. Other methods are to suspend it on ligaments or inthe case of a very thin coil I may attach one or more points rigidl to theouter pole, the inner pole or the re ecting surface, by means of clamps, and the sound absorbing material situated in the cavity may or may not touch the coil itself.

, What I claim is 1. In non-resonant means for reproducing sound, the combination of a field magnet,

a conducting element having a freely exposed surface, such, conducting element being aperiodically mounted in relation to its supporting structure, a non-resonant reflecting barrier set to the rear of the said conducting element, partial access of the sound waves to the rear of the conducting element being possible, and an electric circuit connected to the conducting element.

2. Innon-resona nt means for reproducing sound'asclaimed in claim 1, the insertion of a sound absorbing medium, such as lushvelvet or cotton wool, between the sai conducting element and the reflecting barrier.

3. In non-resonant means for reproducing sound as claimed in claim 1, the insertion of .a sound absorbing medium, such'as plushvelvet or cotton wool, between the said conducting element and the reflecting barrier, and mounti the conducting element on the sound absorbmg-medium.'

4. In means for reproducing sound, the combination of a field magnet with an annular magneticair gap, the winding of which constitutes a reflecting barrier, an annular conducting element. in effect non-resonant and aperiodlcally mounted, and a free passage way on one or both sides of the ele- 1 ment.

'5. In means for re roducing sound, the fibrous character, such as cotton wool, and combination of a totally enclosed field maga free passage way on one or both sides of. net With' an annular magnetic air gap, the the element. l Winding of which constitutes a reflecting In testimony that I claim the foregoing W barrier, an annular conducting element in as my invention I have signed my name this efiect non-resonant, and aperiodically mount- 11th day of July 1924. ed on a pad of sound absorbing material of ADRIAN FRANCIS SYKES. 

